1. Technical Field
The present invention relates to a yogurt with reduced water activity. The invention also relates to food products that comprise a yogurt with reduced water activity. Examples of food products made with reduced water activity yogurt include but are not limited to food bars, cookies, bakery products and cereals, including but not limited to breakfast cereals. In comparison to food products made using conventional yogurt, products made using reduced water activity yogurt have greater microbiological stability, slower rates of degradation processes, and longer shelf lives.
2. Background
Food products comprising yogurt are preferred by many consumers for yogurt's health and taste benefits. For example yogurt has health benefits associated with milk, such as calcium for strong bones. Live cultures present in yogurt are another potential benefit. In addition, the texture and mouthfeel of a product like yogurt can also make it more desirable. For example, U.S. Pub. No. 2011/0250327 to Smith et al. describes an effort to produce a chewy and intermediate moisture bar resembling the texture and mouthfeel of candy bars.
With respect to yogurt specifically, there has been an industry-wide desire by food product manufacturers to include yogurt in the formulation of food products for its taste, texture, mouthfeel and health benefits. However, when dairy components are added to a product, spoilage can be a problem. For example, U.S. Pat. No. 7,351,439 to Zukerman et al. describes a dairy product that must be stored refrigerated or frozen.
Apart from refrigeration, one potential solution to spoilage is heating a product to dehydrate it, but dehydration can result in undesirable textural changes in a product. For example, chewy bars tend to have water activities in the range of 0.3 to 0.65. Dehydrating one of these chewy bars will often result in a bar with a lower water activity, which is correlated with firmer or crunchier bars. For example, Smith et al. notes that crunchy bars generally have water activities of less than about 0.5 and, in some cases, around 0.2 to 0.3.
Another potential solution to spoilage and an alternative to using a dehydrated bar is a fully-cooked bar with a water activity that is somewhat higher than the water activities of crunchy bars. U.S. Pub. No. 2011/0244091 to Zukerman et al. describes a process for producing yogurt and cereal bars, rice pudding bars, and milk and cereal bars that provide handheld milk and cereal breakfasts that are fully cooked and have water activities that are higher than 0.85. However, using a higher water activity is problematic because pathogenic microorganisms can survive at water activities above about 0.85. For example, Staph aureus will grow at a water activity of about 0.86.
Another means of reducing water activity that avoids dehydration is increasing the solids concentration of a product. One example of a high solids dairy-based food can be found in U.S. Pat. No. 7,842,325 to Fitzsimons et al. Fitzsimons et al. describes a method of making a high solids, high protein dairy-based food, but it is preferably used for a cheese or cheese-like product having a protein to water ratio of between 0.6 and 3.0. Furthermore, the dairy-based food of Fitzsimons et al. is made from a milk protein concentrate containing at least 60% protein by weight on a solids non-fat basis. As is evident in Fitzsimons et al., at this solids concentration, a dairy product tends to have the consistency of a hard cheese or cheese “crumble”, not a yogurt.
In the context of yogurt, it is desirable to obtain a product resembling the taste, texture and mouthfeel of real, fresh yogurt while avoiding spoilage problems. Currently, the addition of yogurt to a product is accomplished by adding powdered yogurt, typically resulting in a finished product with a concentration of powdered yogurt of about 1-3% by weight (“wt %”). The powdered yogurt can be added directly to the food product or added to a compound confectionery coating which is then applied to the food product. But the use of powdered yogurt can result in a less desirable texture and mouthfeel as compared to the use of real, fresh yogurt.
Although more desirable in some aspects, simply adding fresh yogurt to a product is also a generally unviable approach. One potential problem when adding real, fresh yogurt to starch-based (e.g., grain-based) food products is the difference in water activity (aw) between the two components, which can result in a final product with a higher than desirable water activity. For example, yogurt typically has a water activity of about 0.99; whereas, bars typically have water activities ranging from about 0.1 to about 0.7. After combining yogurt with a grain-based component in a bar, the two components will equilibrate to a common water activity unless they are physically separated with a moisture barrier layer. Typically, the equilibration of water activity results in a bar with a water activity too high to be microbiologically stable. Also, the mixing of the cultured yogurt component with grain-based components presents the opportunity for contamination of the yogurt with undesirable microorganisms from the grain-based components. As used herein microbiologically stable is defined as free of microbial spoilage due to growth of bacteria, yeasts, or molds throughout the intended shelf life. Although these problems have been discussed in the context of a starch-based component (e.g. a grain-based component), similar problems can result from combining a protein-based component with a yogurt component.
One method of addressing the problems that result from adding real, fresh yogurt to grain-based foods is physical separation of the two components. This involves the use of a moisture barrier that completely separates the yogurt and the grain-based component. An example is the granola component on top of a cup of yogurt. The granola component is physically separated from the yogurt until the consumer mixes the granola component into the yogurt prior to consumption.
While physical separation theoretically allows consumers to combine a real, fresh yogurt component and a grain-based component, it has several disadvantages. First, the use of a barrier layer limits product configuration. For example, a non-edible barrier layer is incompatible with products in which the yogurt component is in direct contact with the grain-based component. Specific examples include bars, cookies, bakery products and cereals. Also, a non-edible barrier means that the product is not ready-to-eat. The consumer must do something, for example, removing the barrier layer and mixing a yogurt component and a granola component, prior to eating the components. Although at first glance this may appear to be a small inconvenience, for some consumers it is a serious problem. For example, it can be a key consideration for consumers of hand-held foods such as bars and baked goods. A second problem with the use of a barrier layer is that it requires additional product packaging. This has several undesirable results, including but not limited to one or more of the following: additional production costs, more manufacturing steps, and additional post-consumer waste.
What is needed is a new and innovative yogurt product incorporating the taste, texture, mouthfeel and health benefits of yogurt, but with greater resistance to spoilage. For example, it would be desirable to have a real, fresh yogurt with a sufficiently reduced water activity to provide enhanced microbiological stability for the yogurt, but without undesirable changes to the taste, texture or health benefits of the yogurt. A yogurt with a water activity of less than about 0.85 is especially desirable, because below that water activity, no pathogens can survive.
However, reducing the water activity of a yogurt can result in potentially undesirable changes in a yogurt. For example, dehydration can cause grittiness, or result in the texture and mouthfeel of a powder rather than fresh yogurt. Accordingly, a need exists for a microbiologically stable yogurt with the taste, texture, mouthfeel, and health benefits of real, fresh yogurt, as opposed to an overly dehydrated, powdered, or fully cooked yogurt. Furthermore, it would be desirable if such a yogurt had a smooth, creamy texture, as opposed to a gritty, hard, or crumbly texture.
Likewise, a need exists for a microbiologically stable food product that comprises both a real, fresh yogurt component and a starch-based component or protein-based component in direct contact. For example, it would be desirable if such a product incorporated fresh yogurt and grain but had a sufficiently low water activity such that it was microbiologically stable without using a barrier layer between the yogurt and grain components.